Screen printing that forms a print film comprising ink, paste, or the like on the surface of a material to be printed using a printing plate (screen mesh) for screen printing can form fine patterns and has high mass-productivity, and hence is utilized in a wide variety of industrial fields.
In the field of electronic part production, a screen printing method may be employed from the points of both precision and mass-productivity. In this field, the demand for forming finer print patterns with high precision has steadily increased due to the recent development of technology to miniaturize the size of the parts.
LTCC is now a popular technology for high-frequency applications used in advantageously preparing 3-D circuits within a ceramic block enabling burying of passive elements such as resistors, inductors, and capacitors. This LTCC approach also allows a number of interfaces and the reduction of the overall substrate size. LTCC technology utilizes highly conductive metal and has a low dielectric constant, low surface roughness, low sintering temperature, and good thermal properties.
Standard screen printing technology has been principally developed for hybrid circuit manufacturing. Hybrid circuits are electronic modules printed on ceramic substrates, a technology in between semiconductor integration and discrete realization on PCB technology, and they are commonly used when electronic modules have to meet high technical requirements. The advantages of screen printing technology are well known: versatility in the conception, miniaturization, and mass production at low cost. The thick film components are produced by screen printing of conductive, resistive, and dielectric layers in order to achieve passive components on an LTCC substrate. Fine line printing is necessary in order to achieve high-component density. Therefore, it is necessary to study the effect of each parameter on printing, which subsequently affects the value of components in the circuit.
In general, screen printing is the basic technology for thick-film microcircuitry. Many variables will affect the screen printing process. The setting of the screen printer is a manual operation, and the quality of screen printed thick film strongly depends on the operator and the process variables. The parameter setting is essential to ensure the desired thickness and the uniformity of the pastes printed on the tape.
U.S. Pat. No. 6,945,167 discloses a screen printing apparatus and method in that in the print parameter setting process for setting print parameters including a squeegee movement speed, a printing pressure, and plate release conditions, a squeegee movement speed at which the squeegee is to be moved is set at the first step, then a printing pressure for realizing a desired cream solder charging state is set at the second step, and then plate release conditions for realizing a desired cream solder transfer state is set at the third step. It does not mention firing, baking, or heating of ceramic printed board, and there is no mention of LTCC or green tape.
U.S. Pat. No. 4,817,524 discloses a method of the present disclosure applicable to a screen printing method for applying an ink to a substrate by placing a screen over the substrate, drawing a squeegee that includes a contact edge over the screen in a flood stroke such that a layer of ink is deposited on the screen, and then drawing the squeegee over the screen in a print stroke with the contact edge in contact with the screen such that ink is forced through the screen onto the substrate. It does not mention LTCC or ceramic printed board.
U.S. Pat. No. 5,699,733 discloses a process that requires firing at low temperature, i.e., 500-600° C. However, the process is directed to increase paste layer thickness by subsequent repeated layering up to 6 layers. There is no mention of 3-D circuit or interconnecting circuit layers as in an LTCC process.
U.S. Pat. No. 5,448,948 discloses a screen printing device for screen printing a thick film ink through a screen so as to form a substantially void-free film on a surface of a microelectronics circuit. It is limited to squeegee design.
U.S. Pat. No. 4,604,298 is directed to the viscosity of conductive ink compound, a high-viscosity gold alloy, firing at 800-900° C. However, there is no mention of ceramics and no mention of 3-D circuitry or embedding of components.
U.S. Pat. No. 7,930,974 discloses vacuum suction holes for affixing an object to be printed. There is no mention of green tape or ceramic being made. Baking is disclosed for electrode material to form electrodes.
U.S. Pat. No. 7,908,964 discloses specifically to the clearance gap between mask and substrate. There is no mention of ceramic firing, baking, or application for green tape.
Chinese Patent No. 101188260 discloses LTCC process for fabricating a square or circular cavity as a base for a high-powered LED to be formed on the LTCC layer prior to screen-printing. There is no mention of any process control parameters for screen printing.
Chinese Patent No. 101777413 discloses a process for forming an LTCC power inductor comprising ferrite magnetic core and mentions the advantages of high-frequency ceramic material and thinner (finer or higher resolution) screen print lines besides other benefits such as less conductor loss, low dielectric constant, better coefficient of heat conductivity and better exothermic property. The process control parameters disclosed here are applicable for a very specific type of device, i.e., for an LTCC power inductor.